This is a medical malpractice ease. The issue that we find dispositive is whether the trial court correctly instructed the jury on the subject of proximate cause. We hold that in an action for medical malpractice when there is evidence of two or more causes that contributed to the damage suffered, for only one of which the doctor is responsible, the proper proximate cause instruction should instruct the jury that any negligence of the doctor was a proximate cause of the injury if it was a substantial factor in bringing about the damage. We specifically reject the inclusion of an instruction under these circumstances requiring the claimant to prove that the injury would not have occurred “but for” the doctor’s negligence.
*592I.
THE BACKGROUND AND PRIOR PROCEEDINGS.
The Fussells were the parents of a child who suffered brain damage at birth. Dr. St. Clair was the attending physician during the delivery. The child subsequently died as a result of the brain damage.
The Fussells sued Dr. St. Clair, contending: (1) the doctor was negligent during the delivery by artificially rupturing Mrs. Fussell’s fetal membranes when the child’s head was too high, thereby causing a prolapsed umbilical cord, and (2) the doctor mismanaged the delivery when the prolapsed cord was discovered. At trial, the Fussells introduced evidence to substantiate these contentions.
The doctor defended on the ground that he was not negligent in rupturing the fetal membranes, that the prolapsed cord occurred independent of any negligence on the part of the doctor, and that the doctor responded properly to the occurrence of the prolapsed cord.
The trial court instructed the jury that if they found the doctor had been negligent during the delivery of the child, they must determine whether the doctor’s negligence was a proximate cause of the injury to the child. The trial court defined proximate cause to mean:
a cause which, in the natural and probable sequence, produced the complained injury, loss or damage, and “but for” such cause, the damage would not have occurred. It need not be the only cause. It is sufficient if it is a substantial factor in bringing about the injury, loss or damage. It is not a proximate cause if the injury, loss or damage likely would have occurred anyway.
During the jury deliberations, the jury sent inquiries to the trial judge concerning the proximate cause instructions. The jury rendered a verdict in favor of the doctor. Six of the ten jurors who signed the verdict also signed a note to the trial judge stating that although they agreed that the doctor was negligent, they were not “totally convinced” that the doctor’s negligence was the proximate cause of the infant’s death.
Following entry of judgment in favor of the doctor, the Fussells moved for a judgment n.o.v. or in the alternative for a new trial. The trial court denied these motions, refusing to accept the Fussells’ argument that the proximate cause instruction erroneously required proof that “but for” the negligence of the doctor, the brain damage and death of the child would not have occurred. The trial court interpreted the note from the jury accompanying the verdict as meaning the Fussells had not proved proximate cause by a preponderance of the evidence. The trial court also ruled that I.R.E. 606(b) prohibited consideration of the note because it required inquiring into the mental processes of the jury in order to impeach the verdict.
The Fussells appealed, stating two issues:
1. Whether the “but for” standard incorporated into the trial court’s instruction of proximate cause was an erroneous statement of the law in a case involving multiple causes.
2. Whether the trial court should have resubmitted this case to the jury with instructions to apply the “more probable than not” standard of proof when the verdict was accompanied by an explanation signed by six of the ten jurors signing the verdict stating that they had reached the verdict because they were “not totally convinced” on the issue of proximate cause.
II.
THE PROXIMATE CAUSE INSTRUCTION SHOULD NOT HAVE REQUIRED THE FUSSELLS TO PROVE THAT “BUT FOR” ANY NEGLIGENCE OF THE DOCTOR THE BRAIN DAMAGE AND DEATH OF THE CHILD WOULD NOT HAVE OCCURRED.
The Fussells assert the trial court should not have included in the proximate cause instruction a requirement that the jury find the damage and death of the child would *593not have occurred “but for” the doctor’s negligence. Under the circumstances of this case, we agree that the instruction was erroneous.
We first point out that the trial court copied the first portion of the current Idaho Jury Instructions (IDJI) 230 in formulating the proximate cause instruction at issue here. The current IDJI 230 also contains a second paragraph that is bracketed to indicate that it may be used in appropriate cases:
[There may be one or more proximate causes of an injury. When the negligent conduct of two or more persons contributes concurrently as substantial factors in bringing about an injury, the conduct of each may be a proximate cause of the injury regardless of the extent to which each contributes to the injury.]
Both the former and the current IDJI 231 state:
MULTIPLE OR CONCURRENT CAUSES
The Committee recommends that no instruction as to multiple or concurrent causes be given.
Comments
These aspects of causation are covered by the definition of proximate causation. Any coverage more detailed is apt to be confusing or incorrect under the comparative negligence doctrine.
I.R.C.P. 51(a)(2) covers the manner in which IDJI should be used:
Use of Idaho Jury Instructions (IDJI). — Whenever the latest edition of Idaho Jury Instructions (IDJI) contains an instruction applicable to a case and the trial judge determines that the jury should be instructed on the subject, it is recommended that the judge use the IDJI instruction unless [the judge] finds that a different instruction would more adequately, accurately or clearly state the law. Whenever the latest edition of IDJI does not contain an instruction on a subject upon which the trial judge determines that the jury should be instructed, or when an IDJI instruction cannot be modified to submit the issue properly, the instruction given on that subject should be simple, brief, impartial and free from argument. When an instruction requested by a party is a modified IDJI instruction, the party should indicate therein, by use of parentheses or other appropriate means, the respect in which it is modified.
In this case, the portion of IDJI 230 incorporated by the trial court into its proximate cause instruction was not applicable to the case presented to the jury. The “but for” requirement was inappropriate for the jury to consider in light of the evidence presented by the parties.
In Everton v. Blair, 99 Idaho 14, 16, 576 P.2d 585, 587 (1978), the Court stated that “[t]he trial court is under a duty to instruct the jury on every reasonable theory recognized by law that is supported at trial.”
Although the evidence presented by the Fussells indicated that Dr. St. Clair’s negligence was the sole cause of the brain damage and death of the child, the evidence submitted by Dr. St. Clair indicated that there was a cause for which Dr. St. Clair was not responsible — an occult (hidden) prolapsed umbilical cord. Dr. St. Clair’s evidence would have supported a finding by the jury that the prolapsed umbilical cord occurred without any negligence of the doctor. If the jury had accepted this evidence and yet had found that Dr. St. Clair was negligent in responding to the prolapsed cord when it was discovered, the jury might have been misled by the proximate cause instruction given by the trial court. The jury might have concluded that the doctor’s negligence could not have been a proximate cause because even if the doctor had not been negligent, the brain damage and death of the child would have occurred. Stated in the same terms as the last sentence of the proximate cause instruction given by the trial court, the jury might have concluded that the doctor’s negligence was not a proximate cause, because the brain damage and death would likely have occurred anyway.
It was not appropriate for the trial court to use the bracketed portion of IDJI 230 *594referring to one or more proximate causes, because there were not two or more persons whose negligence contributed concurrently as substantial factors in bringing about the injury. Also, the comments to IDJI 231 are misleading when there are multiple or concurrent causes in a case that does not involve comparative negligence.
This was a case in which the trial court should have formulated an instruction to submit the issue of proximate cause properly to the jury. The following instruction on proximate cause requested by the Fussells contains some of the elements that should have been included in the appropriate instruction in this case:
When I use the expression “proximate cause,” I mean a cause which, in natural or probable sequence, produces the damage complained of. It need not be the only cause. It is sufficient if it concurs with some other cause acting at the same time, which in combination with it, causes damage.
This formulation of proximate cause was contained in IDJI 230 until it was amended in 1987 to incorporate concepts to which our Court of Appeals referred in Challis Irrigation Co. v. State, 107 Idaho 338, 689 P.2d 230 (Ct.App.1984) and Edmark Motors, Inc. v. Twin Cities Toyota, 111 Idaho 846, 727 P.2d 1274 (Ct.App.1986). We note that Challis was a breach of contract case and that the discussion of proximate cause was dicta. Edmark was a fraud case in which there was only one cause of the alleged fraud.
In Challis, our Court of Appeals stated that the former IDJI 230 “does not make it entirely clear that in order for a concurring cause to give rise to liability, it must be a proximate cause in its own right.” 107 Idaho at 343, 689 P.2d at 235. In Edmark, our Court of Appeals stated that the former IDJI 230 “essentially contains the ‘but for’ requirement, but it is silent as to a ‘substantial factor.’ ” 111 Idaho at 849, 727 P.2d at 1277. We find in our own cases, however, concepts that are more applicable to the circumstances of this case than the current IDJI 230, Challis or Ed-mark.
Formont v. Kircher, 91 Idaho 290, 420 P.2d 661 (1965) was a medical malpractice case in which this Court considered whether the negligence of a doctor was a proximate cause of the loss of a patient’s leg. The trial court, sitting without a jury, found the doctor had been negligent in treating the patient’s leg but the doctor’s negligence was not a proximate cause of the loss. In reversing the trial court’s decision the Court stated:
The trial court in effect did find proximate cause from the chain of circumstances. However, because the defendant did not have the full care of plaintiff, the court concluded there was no proof of proximate cause. In Pigg v. Brockman, 85 Idaho 492, 381 P.2d 286 (1963), this court held that there can be more than one proximate cause of an injury. Therein, this court quoted with approval the following statement from Riddle v. Artis, 243 N.C. 668, 91 S.E.2d 894, as follows:
“ ‘It is elemental that there may be two or more proximate causes of an injury. These may originate from separate and distinct sources or agencies operating independently of each other; yet if they join and concur in producing the result complained of, the author of each cause may be held liable for the injuries inflicted, * * *.’ ” 85 Idaho at 501, 381 P.2d at 291.
The negligence of the defendant concurred in the final result, and the trial court was in error in its conclusion that a causal relationship was not established.
91 Idaho at 299, 420 P.2d at 670.
Applying Formont to this case, if the negligence of Dr. St. Clair concurred in the brain damage and death of the Fussells’ child, proximate cause was established. Formont does not require that proximate cause is established only when there is proof that “but for” the doctor’s negligence, the damage would not have occurred.
Fouche v. Chrysler Motors Corp., 107 Idaho 701, 692 P.2d 345 (1984) was a products liability action brought by Fouche for personal injuries suffered when Fouche’s *595car collided with an unmanned vehicle. Fouche claimed that his injuries were enhanced by malfunctions of his car’s seat belt and collapsible steering column. The trial court ruled that Fouche had not proved that any defects in the seat belt and steering column proximately caused his injuries. In reversing this ruling, the Court said:
Chrysler argues that because Mr. Fouche introduced no expert medical testimony to demonstrate that “plaintiff’s injuries would not have occurred but for the alleged failures of the seat belt and collapsible steering column to properly function ..., the jury would have had to speculate whether plaintiff’s torn aorta and other injuries would have been sustained in the collision even if there had been no defect or whether plaintiff’s injuries were caused solely by the allegedly defective seat belt and steering column.” However, this objection misconceives the proper analysis. The question is merely whether ... the product defect was a substantial factor in causing the injuries suffered. The conduct of the manufacturer need not be the sole factor, or even the primary factor, in causing the plaintiff’s injuries, but merely a substantial factor therein.
107 Idaho at 704, 692 P.2d at 348 (emphasis in original) (citations omitted).
Applying Fouche to this case, the jury should have been instructed that proximate cause was established if the jury found that Dr. St. Clair’s negligence was a substantial factor in causing the brain damage and death of the Fussells’ child. Fouche specifically rejected the “but for” requirement to which the Court of Appeals referred in Ckallis and Edmark.
Considering both Formont and Fouche, we conclude that a version of the former IDJI 230 incorporating the substantial factor requirement would correctly state the proximate cause instruction in this case. The instruction should read:
When I use the expression “proximate cause,” I mean a cause which, in natural or probable sequence, produced the damage complained of. It need not be the only cause. It is sufficient if it is a substantial factor concurring with some other cause acting at the same time, which in combination with it, causes the damage.
Our analysis in this case may seem to be at odds with our recent decision in another medical malpractice case — Hilden v. Ball, 117 Idaho 314, 787 P.2d 1122 (1989). In Hilden, we upheld the giving of a proximate cause instruction that included the “but for” requirement that we have disapproved in this case.
Despite some similarities to this case, Hilden involved only a single force or cause. In Hilden, the patient died from cardiac arrest brought on by lack of oxygen in the heart. The plaintiff alleged that the doctor’s failure to preoxygenate the patient before surgery caused the patient’s death. The doctor’s defense was that the failure to preoxygenate the patient was not a violation of the local standard of health care. The Court specifically held that the trial court was not wrong in viewing the case as a single force or cause case. Id. at 335, 787 P.2d at 1143. In contrast, the evidence presented by the defense in this case would have permitted a finding by the jury of two forces or causes.
III.
CONCLUSION.
Because of our decision on the impropriety of the probable cause instruction, we do not address the second issue raised by the Fussells on appeal. We believe the questions raised by the jury’s note accompanying the verdict are not likely to arise again on retrial.
We reverse the judgment of the trial court and remand for a new trial.
We award costs to the Fussells. Attorney fees on appeal were not requested.
McDEVITT, J., concurs.